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MEMOIR 



ON 



J otmdatim^ tit ^ompraiMe %h f 



EXPERIMENTAL TESTS OF PILE-DRIVING, 



AND 



FORMULA FOR RESISTANCE DEDUCED THEREFROM. 



COMPILED BY 



RICH'D DELAFIELD, Bv't Maj. Gen'l, 

Corps of Engineers, U. S. Army, Member of the L. H. Board. 



Washington, D. C, Deo. 1, 1868. 
PUBLISHED BY ORDER OP THE LIGHT-HOUSE BOARD. 



[REPRINT,] 



WASHINGTON: 

GOVERNMENT PRINTING OFFICE. 



1878. 



K- 



t^ 



M E MOIR 



ON 






EXPERIMENTAL TESTS OF PILE-DRIVING, 



AND 



FORMULA FOR RESISTANCE DEDUCED THEREFROM. 



COMPILED BY 



RICH'D DELAFIELD, Bv't Maj. Qeii'l, 

Corps of Engineers, U. S. Army, Member of the L. H. Board. 



Washington, D. C, Dec. 1, 1868. 
PUBLISHED BY ORDER OP THE LIGHT-HOUSE BOA 



[KJEZPKIIINrT, ] 




WASHINGTON: 

GOVERNMENT PRINTING OFFICE. 

1878. 



<*f* 



H-0^ 



REFERENCES TO AUTHORITIES CITED IN THIS MEMOIR. 



1. Report to Engineer Department, by Captain Delafield, of the Corps of Engineers, July, 

1829, on the Geological Formation of the Outlets of the Mississippi River. — (House 
Document, No. 7, First Session of Twenty-first Congress.) 

2. Comptes Rendus de l'Academie des Sciences. Triger's System for Foundations by 

Pneumatic Pressure. 

3. Crecy's Supplement to his Encyclopaedia of Civil Engineering. London, 1856. Iron 

Cylinders for Foundations sunk by Pneumatic Process. 

4. Hughes' Description of Foundations of Bridge at Rochester, England. Iron Cylinders 

sunk by Compressed Air. 

5. Memoir on Tubular Foundations. Le Pont de la Theiss, Vol. 17. Annales des Ponts et 

Chaussees for 1859. 

6. Pont sur Le Rhin a Kehl, par Vuigner et Fleur, Saint Denis, Paris, 1861. Pneumatic 

System of Foundations. 

7. Annales du Chimie, 1841. Pneumatic Process for Foundations. 

8. Rondelet, L'Art de Batir, Vol. 3. Weight of Massive Structures on Foundations. 

9. Stewart's Dry Docks of the United States. Pile Foundations at Brooklyn, Philadelphia, 

and Pensacola, and Experimental Tests on Pile-driving. 

10. Papers on Practical Engineering, No. 5, by Col. J. L. Mason, U. S. Corps of Engi- 

neers, 1850, on Resistance of Piles to Pressure and Percussion at Fort Montgomery. 

11. Life and Services of Major John Sanders, of the Corps of Engineers, by Lieutenant 

St. Clair Morton, 1861, on Resistance of Piles at Fort Delaware and Experimental 
Tests on Pile-driving. 

12. General McAlester's Report to the Light-house Board on Resistance of Piles at South- 

west Pass and at St. Joseph's Island. Bonzano's Letter of 9th of January, 1868. 

13. General McAlester's Report to the Light-house Board of the 5th of May, 1868. Modifica- 

tions of his Plans for Foundation of Light-house at Southwest Pass, and Views in 
Relation thereto. 

14. State Papers on Commerce and Agriculture. Commissioner's Report on Light-house at 

Mouth of the Mississippi River, built by Latrobe in 1817; also the Constructing Plans 
of the Building, loaned for reference, December, 1868, by Benj. H. Latrobe, Baltimore, 
Maryland. 

15. Records of the Light-house Board, Washington, D. C. Construction of Light-house at 

Southwest Pass in 1831, and at Pass a l'Outre in 1855. 

16. Henry Howard, Architect, New Orleans. Letters to General Delafield, June, 1868, on 

Foundation of a Church and Hotel in New Orleans, and other structures in Louisiana. 

17. Annual Reports of the Chief Engineer, accompanying the President's Message to Congress, 

from 1824 to 1868. On Foundations and their Construction for the Forts in Louisiana, 
on the Rip-rap Shoal, Hampton Roads, and Fort Delaware, Delaware *River. 

18 Records of the Treasury Department. Reports to the Architect from the Constructing 
Engineers on Foundations of Custom-house, New Orleans. 

19. Journal of the Franklin Institute for February and March, 1868. McAlpine's Iron 
Cylinder Foundation, Sunk by the Pneumatic System, modified by him, for the 
Bridge at Harlem, with Notes on Resistance of Iron and Wooden Piles. 

(3) 



20. Report of the Light-house Board, accompanying the Report of the Secretary of the 

Treasury to Congress for December, 1868. Description of Pneumatic Process of 
Constructing Foundation for Waugoshance Light-house, Lake Michigan. 

21. Minutes of Proceedings of Institution of Civil Engineers, Vol. 23. Description of the 

"Wrought-iron Light-house at Ushruffee, Red Sea. 

22. Engineer and Architectural Journal for January, 1868. Description of Wrought-iron 

Light-house for the Douvres, between the Islands of Guernsey and Brehat. 

23. Proceedings of Institution of Mechanical Engineers for 1861. Description of Wrought- 

iron Light-house at Buda, Spain. 

24. Encyclopaedia Americana. Pile Foundations of the City of Amsterdam. 

25. Engineer and Scientific Journal for 1867. On Pile-driving. 

26. Engineer and Architects Journal. On Foundations for Susquehanna Bridge, April, 1867. 

For the Clyde Viaduct, November, 1864. For the Albert Bridge, Saltash, Cornwall, 
1862 and 1864. On Bridge Pile Foundations, November, 1864. Opinions on London 
Bridge Foundations, January, 1858. For Foundations on Compressible Soils and 
Enlargement of the Base, 1857 ; and on the Grimsby Dock Foundations, 1864. 



Memoir on Foundations in Compressible Soils in connection with 
the adoption of a suitable artificial foundation for a light- house 
at the Southwest Pass of the Mississippi river. 

The following notes on the practice and experience of American and 
European engineers on foundations in very compressible soils are collected 
for the consideration of the committee of the Light-house Board, to which 
was referred the different projects heretofore submitted for a foundation 
for a light-house to be constructed at the Southwest Pass of the Mississippi 
river : 

The soundings off the mouth of the river to the westward along the 
Louisiana and Texas coasts, and to the northward along the Chandeleur 
Islands, and thence eastward along the coasts of Mississippi and Alabama, 
all indicate sandy bottom beyond the immediate influence of the rivers. 
The advance of the delta of the Mississippi into the Gulf of Mexico is 
composed of alumina and vegetable matter overlaying this sandy bed. 
The depth of the sand below the waters of the river and gulf appear to be 
beyond our reach as a base on which to rest any artificial structure, and 
the surface of the soil created by the deposits of the freshets is so deficient 
in solidity as to be designated very appropriately "prairie tremblanteP 
We have to combat the difficulties presented by this overlaying compressible 
mass. It is formed during the annual freshets of the rivers by deposits, in 
eddies and slack water, of the matter abraded by the current from the 
shores and banks of the different rivers as their freshets are thrown into 
the Mississippi, and not thrown up or translated along the coast by the 
ocean wave. These deposits from the tributaries of the Mississippi valley 
vary in specific gravity, are deposited during the annual freshets in propor- 
tion to their gravity, and combined with more or less water in the porous 
mass form strata of varying density overlaying each other, and constitute 
the accumulation from year to year. 

A remarkable feature in this alluvial formation is the upheaval by some 
unaccountable power of islands that consist of the deep seated strata, raised 
and forced up many feet above the level of the gulf and annual freshets, 
leaving cavities beneath them, and an element of destruction in the con- 
tinued discharge of matter mixed with water thrown up for an indefinite 
period after their first and sudden eruption and formation. They have 
been sufficiently described in previous reports to the Board, on its files, and 
now only referred to for indicating localities the engineer should studiously 
avoid as beyond his power of adaptation for foundations of heavy structures, 
and, with the previous introductory remarks, to be considered with the 
projects of engineers for other difficult localities now to be noticed. (See 
House Document No. 7. 1st session of the 21st Congress.) 

(5) 



HOLLOW IKON CYLINDERS SUNK BY ATMOSPHERIC PRESSURE. 

This system lias been applied successfully in Europe and America. 
Having been proposed for the Southwest Pass light-house, the following 
notes are submitted explanatory of its advantages and applicability in certain 
localities : 

The first application of this principle is mentioned in Ure's' Dictionary 
of Arts and Manufactures as having been tried on the Loire, in France, 
by Triger, in sinking a shaft 65 feet. A detailed account of Mr. Triger's 
system is to be found in the Comptes renclus de l'Academie des Sciences. 
The principle was applied by Mr. Hughes in sinking the piles at Rochester 
bridge, England. With his modifications it has entirely superseded the 
ordinary diving-bell for foundations in deep water. Compressed air is 
made to free a hollow pile from the water within it after it has been placed 
in its situation, (the bed of the river or other place,) there used as a diving- 
bell, without again being drawn up, and remains as a part of the perma- 
nent structure. 

Mr. Hughes sunk, on the Rochester side of this bridge, 12 cylinders or 
piles, and 30 on the Strood abutment; each pile consisting of 2 or 3 or 
more sections of cylinders, 9 feet in length, 7 feet in diameter, bolted 
together through stout flanges, the bottom having a beveled edge. For 
a description of sinking these piles, see Crecy's Supplement to his Ency- 
clopaedia of Civil Engineering, London, 1856. Mr. Hughes' system is 
admirably shown on a large scale, with all its important details, in a work 
published by him in England. 

The agents of Dr. Potts, as a patentee, introduced it in this country, 
and it was successfully used by Mr. Gwynn for a railroad bridge in South 
Carolina, in a sandy bed of the Pee Dee river. Mr. McAlpine has used it 
with success for a bridge over the Harlem river, N. Y., in a muddy and 
sandy soil, and at this time it is being applied on a more enlarged scale 
under the Light-house Board, by General W. Sooy Smith, in the con- 
struction of a wall around the light-house at Waugoshance, in Lake Mich- 
igan, in a gravelly and rocky bed. 

The Clyde or Nethan viaduct is carried on cast-iron cylinders, sunk in 
the sandy bed of the river, filled up to the level of flood-tide with concrete, 
leaving upwards of 40 feet of the upper portion of the cylinders without any 
filling. (Engineer and Architectural Journal, November, 1864.) 

In the construction of the centre pier of the Albert bridge, at Saltash, 
on the Cornwall Railway, a ivrought-iron cylinder, 37 feet in diameter, and 
90 feet high, open at top and bottom, was sunk through the mud to the rock. 
It was expected that, forming a bank around the cylinder after being sunk 
to the rock, would exclude the water. 



The cylinder was constructed to admit also of air pressure; the surface 
of the rock was inclined 6 feet lower on one side than the other; the iron 
cylinder was shaped to conform with the rock ; a dome or lower deck was 
constructed inside at the level of the mud, 13 feet below the surface of the 
water; and an internal cylinder, open at top and bottom, connected the 
lower with the upper deck of the cylinder; a 6-foot cylinder was fixed 
eccentrically inside the other, and an air-jacket or gallery, making an inner 
skin around the bottom edge below the dome, was formed about 4 feet 
wide, divided in 11 compartments, and connected with the bottom of the 
6-foot cylinder by an air passage below the dome. 

When the 37-foot cylinder was thus constructed, it was towed to and 
accurately adjusted over the intended site ; water was then let in, until the 
cylinder penetrated through 13 feet of mud, and rested on some irregularity, 
causing it to keel over about 1 f 6". By letting water in upon the dome 
or lower deck, and loading the higher side with iron ballast, the cylinder 
forced its way through the obstruction at the bottom edge, and took a nearly 
vertical position. 

The air and water pumps were then worked, and the greater part of the 
mud and oyster shells which filled the compartments of the air-jacket was 
cleared out, and the irregular surface of the rock excavated — the bottom of 
the cylinder being now 82 feet below high-water line. A ring of ashlar 
stone, 4 feet wide and 7 feet high, was then built in the air-jacket, and a 
bank of clay and sand was deposited around the outside of the cylinder to 
compress the mud. 

When the water was pumped out the body of the cylinder below the 
dome, and the excavation of the mud was being proceeded with, a leak 
broke out and the water overpowered the pumps. Recourse to air pressure 
in the body of the cylinder below the dome was determined upon and ar- 
rangements made therefor. 

The 37-foot cylinder was loaded with 750 tons of ballast when the pumps 
succeeded in keeping the water down ; the mud was then excavated, the 
cylinder below the dome securely shored across, and the rock leveled, when 
the masonry was commenced in the body of the cylinder. 

As soon as the masonry reached the level of the air-jacket ring the plates 
of the air-jacket were cut out, and the two masses of masonry were bonded 
and thus united, forming a single mass. Upon the top of the bonding 
course of masonry two courses of brick were laid in cement, making a 
water-tight floor over the whole diameter of the column. 

The next operation was to draAV off the water above the dome and remove 
the ballast, allowing the masonry within to proceed. After the masonry 
had been completed to the plinth course the upper part of the cylinder was 
unbolted at the separate joints and floated to the shore. 



8 

The roadway is 100 feet above high-water mark. This centre pier sup- 
ports iron arches of 455' span each from the centre of the river. (Engi- 
neer and Architectural Journal, 1862 and 1864.) 

Bridge over the Harlem river, on cast-iron cylindrical piles, by Wm. J. 
McAlpine. The draw pier of this bridge was composed of one central and 
ten circumscribing iron columns, each 6 feet in diameter and 50 feet i% 
heighth — the water being 20 feet in the deepest part. These piles were 
sunk by the pneumatic process, (both plenum and vacuum.) It was deemed 
advisable to increase even the large base, due to the size of the column 
formed by these cylinders. 

It had been decided to fill the columns with concrete; and it was sug- 
gested to extend this masonry below the bottom of the iron cylinders, (as 
the men could work in water,) undermining the adjacent earth as far as 
practicable, and to extend the concrete into the space thus undermined. 
This was done in sections of about 2 feet in width ; and, when the rim had 
been completed, it was found that the column was virtually extended, and 
that the water would readily sink, under the pneumatic pressure, to a level 
with the bottom of the concrete, so that the sand within it was easily 
removed, and the space filled with concrete to a depth, generally, of 4 feet 
or more. The cement set with greater rapidity under pneumatic pressure 
than in the open air. 

The last column was driven from 16 to 20 feet, in from 3 to 6 days, in 
sand and porous material, free from obstruction; 12 men, all told, sufficed 
to do the work, including engine-drivers, stevedores, and foremen. The 
metal in the columns was 1 J inch thick. No ill effects were experienced 
by the workmen from a pressure of 2J atmospheres. 

In some cases the pile could be sunk by the vacuum process alone ; in 
all other cases by the plenum, and sometimes both might be employed with 
advantage, and further aided by weight or pressure on the heads of the 
cylinders. 

The support of these iron columns, derived from friction on the exterior 
surface, was found to be J a ton per square foot, but in the finest earth it 
would amount to 3 tons. 

The support from the area of the bottom in shallow depths was from 5 
to 10 tons per square foot. (See Engineer and Architectural Journal for 
January, 1868.) 

This system is perfectly reliable in all cases where the compressible soil 
can be removed and a hard bottom reached on which to found the contem- 
plated structure. It was practiced with great success in the construction 
of the Theiss bridge, and minutely described in the Annales des Ponts et 
Ohaussees, 1859, and Annales clu Chimie, (1841.) Mr. McAlpine gives 
much useful and practical information on this subject in the February and 
March numbers of the Journal of the Franklin Institute. For a founda- 



9 

tion at Waugoshance, Lake Michigan, on this system for a wall of 8 feet 
thick, and laid 12' 3" below the surface of the water, 7 feet of which was 
through gravel and large boulders, enclosing an elliptical area of 67' by 
49', under one wrought-iron cylinder, with air-pumps and valves, see the 
Report of the Light-house Board, accompanying the Report of the Secre- 
tary of the Treasury for December, 1868, pp. 71 and 72. 

PILE FOUNDATIONS. 

The next system for consideration is that of piles driven into the ground, 
on which the superstructure rests directly, or through the intervention of 
a floor of wood or masonry. It is deserving of particular attention from 
its probable fitness for the locality under consideration at the Southwest 
Pass of the Mississippi river. 

FOUNDATIONS ON WOODEN PILES.— AMSTERDAM. 

The most extensive and oldest application of pile-driving for foundations 
to which instructive reference is at command is in the city of Amsterdam. 
The original site of this city was a salt marsh. All the buildings, (28,000,) 
for a population of 224,000 souls, (in 1850,) covering a surface of 900 
acres, are supported on piles of from 50 to 60 feet in length. After passing 
through a mixture of peat and sand of little consistence, at a depth of 
about 40 feet, they enter a bed of firm clay. The ends of the piles are 
sawed level, and covered with thick plank, on which the masonry is con- 
structed. Though the houses have declined from the perpendicular, they 
are considered to be quite secure against falling ; yet such a contingency 
occurred in 1822, by the sinking and total ruin of a large stack of ware- 
houses heavily filled with corn — (wheat in bulk that shifted the weight.) 

The palace built in 1648 is supported on 13,659 piles. It is 282 feet 
long, 235 feet wide, and 116 feet in height, exclusive of a cupola of 41 
feet. 

The steeple of the Oude Kirk is 240 feet high. The surface or level of 
the natural ground is below the level of the ocean. 

FOUNDATIONS ON WOODEN PILES AND CAISSONS IN THE BED OF THE 

THAMES, LONDON. 

The labors of engineers in the valley of the Thames river, at and about 
London, give much useful information in the construction of ancient as 
well as modern pile foundations. 

Old London bridge was commenced in 1176, and finished about 83 years 
thereafter. The piers rested on piles driven only around the outside of the 
pier, so placed as to carry the ichole weight. They were of elm, and at the 
expiration of six hundred years, on being drawn up, remained without 
material decay. A part of this bridge fell about 100 years after it was 
finished; and the whole structure was removed to give place to the new 
bridge in 1825. 



10 

Old Westminster bridge was built between 1733 and 1747. Piles were 
used under one pier only. Its piers (with the one exception) were con- 
structed in caissons or flat-bottomed boats. Each caisson contained as 
much timber as a forty-gun frigate. They were 80 feet long by 30 feet 
wide. These foundations failed ; the caisson bottoms or floors sunk in the 
middle; the sides and ends projecting beyond the stone work broke off and 
bent upwards. The sinking of the bearing area of the substratum, under 
the partial and unequal pressures of the floors of the caissons, has had more 
to do with the failure than any other defect. 

Black Friar's bridge was built between 1760 and 1771. The founda- 
tions were laid in caissons, the floors of which rested on piles about 9 feet 
apart — only 45 piles to each caisson — and intended to obtain a level surface 
on which to rest the floor, to settle down to a uniform bearing. Its sta- 
bility, says Rennie, for many years is to be attributed to these piles. It 
has since failed, and requires large expenditures on repairs. 

It was believed in this case, as at Westminster, that if the scour of the 
river bed could be prevented, and nothing carried away from under the 
foundations and about the piles by external agency, the clay base would 
support the gravel stratum above it, and the gravel the stone; but the 
pressure per foot in the Westminster was nearly 5J tons, and in Black 
Friar's 5 tons per square foot; and clay, when the pressure is at great 
depths within it, will not bear 5 tons per foot. 

Waterloo bridge, built between 1809 and 1817. The foundations of the 
piers of this bridge are built in coffer-dams or caissons, the floors of which 
rest on piles, about 3 feet apart, under the entire base of the pier, penetra- 
ting the clay about IS feet The foundation is arranged with plank, con- 
crete, and stone, as in the New London bridge. The estimated pressure 
per foot on the head of each pile is, in this case, about 68 tons. The arches 
are 120 feet span, and weigh about 2,500 tons each. 

Vauxhall bridge was built between 1811 and 1816. The foundations 
of the piers of this bridge were built in caissons. An excavation was made 
down through the gravel stratum to the clay. It is a light structure, and 
no settlement is recorded. 

New London bridge, built between 1825 and 1831. The foundations 
of the piers of this bridge are built in coffer-dams or caissons, the floors 
of which rest on piles under the entire area of the bases of the piers. The 
piles are about 20 feet long and 3 feet apart, penetrating the clay 18 to 19 
feet. On the heads of the piles were laid sleepers ; the loose earth between 
the heads of the piles is replaced with rubble concrete, on which blocks of 
stone and brick work filled up the spaces between the pile heads and imme- 
diately over the platform of oak planking which carried the first course of 
granite. 



11 

The pressure upon each pile is 80 tons, or 5 tons per square foot of the 
entire area of the pier. ' Each pier of this bridge settled from six to ten 
inches towards the down stream. No further settling is apprehended. 

Hungerford bridge, built in 1844. This is a chain suspension bridge. 
On the Hungerford market side the ground under the mooring piers was 
very bad. Piles were here driven to the depth of 30 feet. 

Chelsea bridge, built between 1850 and 1857. This is a suspension 
bridge. The foundations of the piers are on bearing piles of 14 inches 
square, 3' 6" apart, and driven 32 feet below low water, and about 16 feet 
into the London clay. (For other details of these foundations see Engineer 
Architectural Journal, for November, 1864.) 

New Westminster bridge, built in 1858 and since. The arches of this 
bridge are of wrought and cast-iron. Elm piles, 32 feet long, are driven 
in alternate rows of 3 and 5 each, to the number of 145 in each pier, and 
18 to 20 feet into the London clay, each tested to a bearing weight of 60 
tons. Circumscribing the area into which the elm piles are driven, hollow 
cast-iron piles, 15 inches diameter, 25 feet long, are driven 4 feet apart, 
and between these, in grooves cast on hollow piles, flat iron piles are driven 
to nearly the same depth, forming a coffer-dam, within which all the soil 
overlaying the gravel bed is excavated, and concrete filled in to the top of 
the piles, which are cut off 6 inches below low water. 

On the heads of the elm piles is a course of stone covering two or three 
piles cdternately, upon this the bottom course of granite of large size is laid. 
The bearing piles are 14 inches square, driven at intervals of V 9" from 
centre to centre, to an average depth of 20 feet in the London clay. It 
will thus be noticed that the solid stone piers sustaining the iron arches rest 
upon the heads of the wooden piles, which stand a considerable height above 
the bed of the river; that these piles are within an enclosure of cast-iron 
and granite slabs; and around the piles and filling up the sides of the 
casing or enclosure there is a solid bed of concrete as good as rock. 

At the Hull docks the load per pile T)er square foot is 37 tons; at the 
London bridge the load per pile per square foot is 80 tons ; at the Albert 
warehouse, Liverpool, the load per pile per square foot is 80 tons; and at 
the New Westminster bridge it is 12 tons per square foot. And the pres- 
sure on the whole area of the foundation is only 2 tons, while on the old 
bridge it was 6 tons, and in the London bridge it is 5J tons. 

REMARKS OF ENGLISH ENGINEERS ON THE LONDON BRIDGES. 

The bed of the Thames is much lower than when the bridges winch have 
failed were built, occasioned by the increased scour produced by removing 
the old London bridge. Whenever the foundations have been made to 
depend on the gravel, and have not been taken deep into the London clay, 
failure has taken place. In the clay only can a foundation be found. 



12 

The old successful examples are all of one class — coffer-dam examples, 
(excepting Vauxhall and Mr. Page's recent structures.) Vauxhall was a 
coffer-dam carried to the clay without piling ; the weight of the bridge not 
needing piles. 

All the other sound bridges are piled deep into the blue clay. The 
shoulders and sides of these piles, and the surface of the clay between them 
at their tops, are the ultimate bearing points, upon which presses the super- 
structure, whether of granite or other stone courses, or composed of concrete 
and wood or of iron. 

The concrete and iron casing about the piers of the Westminster is believed 
to be a ten times stronger medium, for the retention of the piles in their places, 
than the London clay (at whatever depth) would be ; and omitting, therefore, 
all aid from the external piles and casing in bearing the weight, we find that 
the 133 elm-bearing piles are alone capable of bearing a load four times 
greater than can be put upon them, and there is not so much chance for un- 
equal settling as with sleepers and bearing planks, such as exist at the 
successful bridges. We cannot find one instance of deep-piled bridges abroad 
which has fallen. 

In Venice the piles are covered with a planking of flat-boards under 
water. Whilst the London clay would only bear a pressure of 5 tons per 
foot, piles driven into it would carry 70 to 80 tons. 

At the Hull docks the piles were 10 inches in diameter and carried a 
weight of 37 tons per foot superficial; at the London bridge the piles were 
10 inches in diameter and carried a weight of 80 tons per foot; at the 
Albert docks, Liverpool, the piles sustained a weight of 80 tons per foot; at 
the New Westminster bridge the piles were 14 inches in diameter, and 
would have to carry only 12 tons per foot. It was stated that the elm 
piles used in the foundations of Westminster bridge would carry 200 tons 
without permanent deflection. (See Engineer and Architectural Journal, 
for 1858.) 

The compressibility of oolitic and tertiary clays can only be overcome by 
piling, deep sinking, heavy ramming, or heavy weighting. The point of 
bearing must be carried below the possibility of upward reaction. The 
depth of a foundation in compressible ground ought not to be less than J 
the intended height of the building above ground — that is, for a shaft of 
200 feet the foundations should be made secure to a depth of 50 feet, by 
piling or by well sinking and concrete. (Engineer and Architectural 
Journal, for 1857.) Masses of concrete, brick or stone, placed on a com- 
pressible substratum, however cramped and bound, may prove unsafe. 
Solidity from a considerable depth can (done be relied upon. Mere enlarge- 
ment of a base may not in itself be sufficient. (Engineer and Architectural 
Journal, for 1857.) 



13 

FOUNDATIONS OF THE GEIMSBY DOCKS ON THE HUMBER, 

These docks were commenced in 1846. The entrance to them is beyond 
the low-water line, and advanced into the river j of a mile. The ground 
over the whole area of the two entrance locks, centre pier, and wing walls 
was excavated 8 feet below the sill of the larger lock, and bearing piles 
were driven in rows 5 feet from centres, and in some places 4 feet over the 
whole area. A pile was considered sufficiently driven when it moved not 
more than J of an inch with the blow of a ram of 1 ton falling 12 feet. 
The heads of the piles were then cat off to a uniform level, the ground was 
removed to a depth of 2 feet below this level, and the spacefilled with concrete. 
Timbers so connected as to form continuous ties across the locks and centre 
pier were then laid transversely in parallel rows on the bearing piles. Other 
similar timbers were laid at right angles to the transverse bearers, concrete 
being filled in to the upper surface of these longitudinal bearers, which 
were then covered with planking as a bed for the masonry. (Engineer 
and Architectural Journal, for 1864.) 

The result of European experience gives the following as the bearing 
weights supported by the foundations of the piers of several of the most 
remarkable and heaviest structures, in pounds per square foot : 

Dome of St, Peter's, Kome 35,254 lbs. 

Dome of St. Paul's, London 41,713 lbs. 

Dome of the Invalid, Paris 31,862 lbs. 

Dome of the Pantheon, Paris 43,440 lbs. 

Column of the Basilica of St. Paul 42,950 lbs. 

Steeple of the Church of St. Mary 63,325 lbs. 



For the relation between the total surface covered and the part occupied 
by its walls, or the supporting parts and the above, see Rondel et, Vol. 3, 
p. 232. 

PRACTICE AND EXPERIENCE OF UNITED STATES ENGINEERS. 

We now proceed to give the practice and experience of the Engineers of 
the United States in the construction of foundations in different localities 
and in compressible soils. The dry dock at the Brooklyn Navy Yard, 
New York, was commenced in 1841 and completed in 1851. It contains 
13,837 cubic yards of masonry, resting upon 38,532 cubic feet of pile 
timber. 

The soil was found to be chiefly vegetable decomposition to the depth of 
10 feet, and below this almost impalpable quicksand containing a large 
proportion of mica. When confined, and not mixed with water, it is very 
firm and unyielding, presenting a strong resistance to penetration. When 
saturated with water it becomes a semi-fluid, and moved by the slightest 



14 

current of water passing over or through it. Small veins of coarse sand 
were also occasionally encountered', through which flowed springs of fresh 
water. Borings were made to the depth of 80 feet, and brought up sand 
and clay and fresh water. There is but a small proportion of clay in any 
part of the foundation. The borings extended 40 feet below the founda- 
tion of the dock. 

The foundations for the superstructure of this dry dock were placed 37 
feet below mean tide and 42 feet below the surface of the ground. Black 
mica overlaid the quicksand under the coffer-dam. Under and in this 
coffer-dam 3,504 piles were driven, averaging 39 feet in length by 15 
inches square. 

The earth above low water was removed before the coffer-dam was 
formed, and about 10 feet in depth was removed by dredging. The semi- 
fluid state in which the material was found, after the water had been 
pumped out of the pit, was very difficult to remove. It was so fluid as to 
require tubs for its removal. Bottom springs of fresh water were found in 
about six feet of the required depth of the foundations. The largest dis- 
charged 10 gallons per minute. When flowing from a level of 26 feet 
below low water it discharged 38 gallons per minute, containing 27 ounces 
of sand; at a level of 22 feet it discharged 33 gallons per minute, contain- 
ing 17 ounces of sand; at a level of 17 feet it discharged 10 gallons per 
minute, unmixed with sand. 

These springs presented great difficulties in laying the foundations from 
the flowing of the water, which as it came up brought large quantities of 
sand, which, if continued to flow, would soon have endangered the sur- 
rounding works. The pressure of the water was so great as to raise the 
foundation however heavily it could be loaded. 

The settling of the piles supporting the pump well was the first evidence 
of undermining from one of these springs. The site of the well was 
changed, but the spring followed and compelled another change of the well. 

This spring was driven out of the old well by driving piles until it was 
filled up, but it immediately burst up among the foundation piles of the 
dock near by. In a single day it made a cavity in which a pole was run 
down 20 feet below the foundation timbers. 150 cubic feet of stone were 
thrown into this hole, which settled 10 feet during the night, and 50 cubic 
feet more were thrown in the following day, which drove the spring to 
another place, where it undermined and burst up through a bed of concrete 
2 feet thick. This new cavity was repeatedly filled with concrete, leaving 
a tube for the water to flow through ; but in a few days it burst up through 
a heavy body of concrete in a place 14 feet distant, where it soon under- 
mined the concrete, and even the foundation piles, which settled from 1 to 
8 inches, although 33 feet long and driven by a hammer of 2,200 lbs. falling 
35 feet at the last blow, with an average of 76 blows to each pile, the last 



15 

blow not moving the pile J an inch. It was then determined to drive as 
many additional piles into the space by means of followers to force those 
already driven as deep as possible. 

The old concrete was then removed to a depth of 20 inches below the 
top of the piles. An area of abont 1,000 square feet around the spring was 
then planked, on which a floor of brick was laid in dry cement, and on 
that another layer of brick set in mortar. The space was next filled with 
concrete, and the foundations completed over all. ' Several vent holes were 
left through the floor and foundations. After a few days, when the cement 
had well set, the spring was forced up to a level of about. 10 feet above the 
former outlet, at which it flowed clear without sand. 

Two other of these springs were closed by freezing in 1848, and forced up 
in one case 800, and in the other 1,200 square feet of the foundations. This 
took place between the lower timbers and the planking, lifting also the first 
course of the stone floor, which was from 12 to 15 inches thick. 

The whole number of bearing piles in the foundation is 6,549. They 
are chiefly round spruce timber 25 to 40 feet long, averaging 14 inches 
diameter at the head. The average length of all the piles driven was 32' 7 /r . 
The piles were originally driven 3 feet from centres. Afterwards as many 
piles were driven as could be forced into the earth. Whenever a hammer 
of 2,000 lbs. weight, falling 35 feet, drove the pile for the last few blows 
exceeding 3 inches per blow, another and larger pile was driven along side. 

With the exception of 541, all these piles were driven by hammers from 
2,000 to 4,500 lbs. each, falling from 35 to 40 feet. The average number 
of blows per pile was 151 with the small hammers, and 50 blows only per 
pile with the large hammers. The 541 piles were driven with a Nasmyth 
steam-pile engine. 

A trial round pile of (20") twenty inches diameter at the butt, and (14") 
fourteen inches at the small end, of 49 feet in length, was driven by a 
2024-lb. hammer, falling finally 35 feet; forty-five feet below the founda- 
tions. The first 100 blows the hammer fell but a few inches; the next 260 
blows drove the pile 30" in 46 minutes; the next 260 blows drove \" to \\" 
per blow for 60 minutes; the next 110 blows averaged \\ n per blow for 
60 minutes, the hammer falling the last blow 34 feet. 

This trial pile suosequently received 200 blows through the medium of 
a follower which drove it an average of \ an inch to each blow. 

Another trial pile was driven 43 feet by a Nasmyth steam-pile driver, 
and then another pile 15 feet long, driven on top of the first, making a 
total penetration in the earth of 57 feet. 



16 
The first pile was driven 42 feet by 373 blows in 7 minutes, as follow: 



4 blows 


, 4 inches each, 


8 " 


3J 


cc 


22 " 


3 


cc 


25 " 


2 


cc 


40 " 


li 


cc 


56 " 


n 


u 


32 " 


ii 


u 


64 " 


li 


a 


73 " 


l 


cc 


49 " 


* 


cc 



The second pile was driven 15 feet by 2,400 blows in 43 minutes, as 
follows : 



33 blows, f of an inch each blow. 

*7Q CC 1 CC CC CC 

100 " i " " " 

800 " drove it altogether 88 inches. 

300 " " " 24 " 

300 " " "• 12 " 

450 " " " 11 " and the last, 

350 " " " 5J " 

The movement of these piles indicated the continuance of the same ma- 
terial to the depth which they reached. 

The foundation was mostly laid as follows : The excavation being com- 
pleted to the proper depth, and piles cut off to a uniform level, 2 feet in 
thickness of concrete was rammed between the bearing piles. These piles 
were then capped with 12 and 14 inch yellow pine timber, laid transversely 
with the axis of the dock, and treenailed to each pile. The concrete was 
then raised to the top of these timbers, and a light flooring of three-inch 
yellow pine plank was laid upon and spiked thereon. Another course of 
similar timber was then placed upon this floor, breaking joints with those 
below, to which they were treenailed. The intervals were next filled with 
concrete, and another floor of 3-inch plank spiked down ; which completed 
the foundation. 

The amount of work done by the heavy Nasmyth hammers was at least 
J greater than that done by those whose hammers were only J the weight. 
This Nasmyth hammer, of 4,500 fibs., was worked with very short rapid 
blows, raised a height equal only to the stroke of the engine. 

The support of this foundation is derived mainly from the adhesion of 
the material into which the piles were driven and slightly from their sec- 
tional area. 



17 

It was ascertained that it required a weight of 125 tons to draw up one 
of these piles, or rather to start or put it in motion, when driven 33 feet 
to the point of ultimate resistance, with a ram of one ton falling 30 feet at 
the last blow. The piles averaged 12" in diameter in the middle, making 
at least a support of 100 tons per square foot of foundation. 

PILE FOUNDATIONS AT THE PHILADELPHIA NAVY YARD. 
At the site of the dock of the Philadelphia navy yard, commenced in 
1849, the first stratum of soil is a mud of rich loam extending from a little 
above low- water level, declining toward the bottom of the river, which is 
of a clean gravel, to the depth of about 24 feet below ordinary low tide, 
w and evidently the deposit through a long period of years of the earthy mat- 
$f ter held in suspension by the waters of the Delaware river, upon a stratum 
of sand and gravel forming the bed of the river. The sand and gravel are 
not more than from 4 to 7 feet in thickness, before those substances become 
mingled with paving stones, large boulders, and to some extent with 
clay, forming a species of hard pan, to which all the piles used in the con- 
struction of the foundations of the work were driven. The object of the 
' foundation of the basin of the dock was to give support to its bottom and 
to secure its outer edge against the action of the current of the river. As 
the excavation was completed, piles were driven 4 feet apart from centres 
in rows from one end of the space to the other. An extra row was driven 
under the line of the walls of the three sides of the basin. A space was 
then formed by drawing a line of sheet piling eight feet from the inner line 
of piles of the coffer-dam. Two extra rows of piles were driven within 
this space, which was then filled with concrete to within 2 feet of the floor 
of the basin. The piles thus driven were cut off to the same level, capped 
with timbers one foot square, and the spaces between these capping timbers 
filled with earth and concrete. (Stewart's Dry Docks of the U. S.) 

PILE FOUNDATIONS AT THE PENSACOLA NAVY YARD. 

The dock at the Pensacola navy yard was built in 1851 and 1852. The 
soil of this locality is clean white sand to a depth of about 40 feet, resting 
upon a bed of soft clay. The sand is so open and porous that a cubic foot 
of it, when saturated, contains 6 quarts of water. 

A space of 140 feet wide by 380 feet long was inclosed by driving yel- 
low pine piles, 12 inches square, to the depth of about 20 feet into the 
sand, placed in contact with each other, for forming a coffer-dam. Within 
this space, secured by other means against filtration, the sand was excavated 
to a depth of 14 feet below tide. 

After a section of the pit had been excavated to the level of the founda- 
tions, the bearing piles were driven in rows 4 feet apart, and 4 feet from 
centres in each row, until a ram of 2,200 pounds, falling 30 feet, could not 
move them more than J an inch. Upon the transverse rows of piles, cap 
2 



18 

timbers, 12 inches square, were placed, and the space between the timbers 
filled with sand. The timbers were then covered with 5-inch plank, spiked 
to the caps, and the whole floor caulked with wedges. On this floor the 
masonry of the basin was commenced. This foundation was tested and 
found satisfactory. The experimental tests showed that a single founda- 
tion pile, as a fulcrum, sustained nearly 39 tons without settlement; and it 
required 41 tons strain to draw a pile that had been driven 16 feet into 
the sand. 

The railroad bridge at Havre-de-Grace, on the Susquehanna river, was 
commenced in October, 1862, and finished in November, 1866. 

The foundations of the piers of this bridge are referred to as examples 
of piles driven in the compressible bed of the river, supporting an iron 
caisson on a grillage of timber resting on the piles, and a caisson lowered 
to solid rock through 15 feet of compressible soil. 

In 1863 piles were driven and sawed off 40 feet below the surface of the 
water for the foundation of pier No. 3 ; a platform or grillage of timber, 
strongly ironed, upon which the pier was to rest, was constructed near the 
site of the work and floated over the site of the foundation under which the 
piles had been driven. This platform was placed between two substantial 
construction piers of timber ; lowering screws, 6 in number, of 3 J inches 
diameter, were attached by hooks to the platform; and to the construction 
piers a section of an iron caisson was constructed, resting upon the wooden 
platform thus suspended. The masonry was then built within the caisson, 
lowered by means of the screws as it approached the top of the section, 
when a second section of the iron caisson was added, built within and low- 
ered by the screws in like manner as the preceding, and thus continued 
until the grillage or wooden platform rested upon the heads of the piles. 

Another pier (No. 7) was founded on the rocky bed of the river under- 
laying the compressible bed of the stream for a depth of 15 feet. This 
latter had been displaced in several places by the spring freshets of 1865, 
rendering piling impracticable; all the earth was, in consequence, removed 
down to the surface of the rock. At the site of this pier the rock bed 
was 18 feet below the original undisturbed bed of the river. To remove 
this earth a wrought-iron foundation caisson, averaging 8 feet in height 
and about 50' by 20' square, was lowered so as to enclose the site of the 
pier. This was gradually depressed to the rock by removing the earth 
within it by means mainly of powerful pumps, aided by the constant exer- 
tions of skilled divers. The masonry was then laid within the tank upon 
the solid rock, and being brought to a level some feet below the top of the 
foundation caisson ; the caisson of the pier resting upon the platform of 
timber was lowered and built upon. The foundation of this pier was 36 
feet below low water. (See Engineer and Architectural Journal, April, 
1867.) 



19 

RESISTANCE OF PILES TO PRESSURE.— FORT RICHMOND. STATEN ISLAND,! 

NEW YORK. 

The soil of part of the foundations of Fort Richmond, now Fort Wads- 
worth, on being excavated to low- water level, was found to be very com- 
pressible, with springs discharging large quantities of water. The scarps 
and counterscarp of the southern half of the land front and face of the 
adjacent bastion of the water front were situated on such a soil, resembling 
that of the dry dock at Brooklyn. The weight to be sustained was a 
granite casemated • battery of four tiers of 8 and 10 inch guns, with the 
shot, shell, and other munitions therefor. The scarps, .piers, and arches, 
are all of granite. 

Piles were in this case resorted- to, and no settlement has since been 
noticed. The work was commenced in 1856, and finished to receive its 
armament in 1861. The piles were 30 feet long, 12 inches square at the 
head, and not less than 10" at the small end. They were driven by a 
hammer of 1,800 pounds weight, with blows in quick succession, the last 
blow of the hammer being from a height of 45 feet. They w T ere cut off 
level with the surface of the ground, and capped with large flat stone, 
covering the heads of from 3 to 5 piles — the joints being filled with con- 
crete, well rammed. A second layer of large flat stone, breaking joint 
with the first, on which the masonry of the granite scarp was commenced. 
It will be noticed that there was no timber grillage covering the heads of 
these piles. 

RESISTANCE OF PILES TO PRESSURE.— EXPERIMENTAL TESTS AT 

PENSACOLA. 

In 1851 a series of experiments were made, under the direction of a 
special board of officers, on the resistance, etc., of the piles driven for the 
foundations of the dock of the navy yard at Pensacola. A pile that had 
been driven six days, surrounded by other piles 4 feet distant from cen- 
tres, of 30 feet in length, averaging 13 inches diameter about the middle 
of its length, round, with bark on, was first selected for these experiments. 
The average depth of the pile in compact sand was 15 feet, driven by 
a hammer of 4,087 pounds, and 69 blows at the rate of 2 J blows per 
minute. 

The first experiment, made on the 17th of May, was the application of 
a power (by pressure or loading) of 23,850 pounds to a pile for 5 minutes, 
which it bore without moving. The second experiment was by applying 
a power of 20,000 pounds to another pile ; a third pile was subjected to 
the same strain for 5 minutes, and a fourth pile resisted the same power for 
5 minutes. There was then applied to this last pile 31,360 pounds (14 
tons) for several minutes. Three other piles were subsequently tried, and 
each resisted 22,400 pounds (10 tons) pressure for 5 minutes. 



20 

The next test was by pulling up the piles, beginning with 22,400 
pounds, applied to the pile ~No. 4, before noted, increasing the power one 
ton every two minutes — that is, after 10 tons had been applied for 2 
minutes; then 11 tons were applied for 2 minutes; then 12 tons, and so, 
until 15 tons, or 33,600 pounds, pressure had been tried, when a hook of 
the steelyards broke. Three days afterwards the experiment was resumed, 
beginning with 10 tons, gradually adding ton by ton, until there was 31 J 
tons of upward strain' acting upon the pile. This experiment lasted 1 
hour and 40 minutes, during which time the power upon the pile was 
constant. 

There was afterwards a gradual increase of power to 39 tons without 
moving the pile. It then resisted 40 tons for J a minute, when it began 
to rise slowly. 41 tons were then applied for If minutes; then 41 J tons 
for half a minute, the pile meanwhile moving upwards at the rate of ^ 
of an inch per minute. The tests of 40, 41, and 41 J tons occupied half 
an hour, during which, the strain being constant, the pile was moved 2J 
inches. 

It was then subjected to a strain of 30 tons for 18 hours, and was not 
moved by it. After which, by adding from 2 to 7 tons, the pile was moved, 
in one hour, three (3) inches; and, after it had moved upwards about 6 
inches, a power of 25 tons was allowed to remain on it for 2 days and did 
not move it. The pile was then withdrawn from the sand. Its extreme 
length was 29 feet. The length of the part which had been in sand was 
16 feet, including the sharpened end of 2 feet in length; 1 foot in depth 
about this pile was loose sand, which had been once excavated and fallen 
back. The average diameter of the part in the sand was 13^ inches, in- 
cluding the bark. The bark remained on the entire pile, except on 3 J feet 
of its pointed end. This pile weighed 1,632 pounds. 

A single pile used as a fulcrum for the lever sustained at the most, dur- 
ing the experiment, 38^^ tons weight without settlement. Experiments 
showed that piles which one day penetrated ^- of an inch per blow, of a 
4,087 pounds hammer, falling 10 feet, was found to penetrate J, \, and ^ 
of an inch by 3 similar and successive blows applied the following day — 
the three blows being given in 1 minute. If the pile is allowed to remain 
undisturbed a short time the power to move it afterwards is greatly increased. 
(Stewart's Dry Docks of the United States.) 

McALPINE AND SANDERS' FORMULA FOR BEARING WEIGHT OF PILES. 

The formula deduced by the engineer, Mr. McAlpine, from his labors 
at the Brooklyn navy yard, applicable to rams of 1,000 Bbs. to 3,000 lbs., 
falling from 20 to 30 feet, was x = 80 (W + .0228 V F— 1.) In which x 
was the supporting power of a pile driven by the ram W, falling a distance 
F ; x and \V being in tons, and F in feet — and that not more than J of the 
result given by this experience should be borne or relied upon for any piles. 



21 

Major Sanders' formula, deduced from his experience in driving piles at 
Fort Delaware, with a ram of 3,500 lbs., falling 3J feet, driving a pile 4'. 2 ; 

R h d 
is 3500 x 42 + 4/.2 = 35000 = 4375 Jbs., the weight which the pile would bear 

8 8 

with safety. (See Stewart's Dry Docks of the United States, and Engineer 
and Scientific Journal, for 1867.) 

FOUNDATIONS OF FOKT MONTGOMERY ON PILES AND GRILLAGE. 

The foundations of Fort Montgomery, on Lake Champion, near the 
latitude of 45°, was commenced in 1844, and the driving of 4,383 piles Avas 
finished in 1846. These piles were capped with a timber grillage in 1848. 
Each pile was calculated to sustain a weight of 7 cubic yards of masonry 
and If yards of earth, or a total weight of 34,125 lbs., or 15.27 tons. 

The piles were driven about 3 feet apart. The grillage is in two courses, 
the lower one, V 3" wide and 12" thick, is notched down 4" on the heads 
of the piles, and pinned thereto. The upper course at right angles to the 
lower one is 12" square across the piles, and 12" X 8" between them, the 
12" X 12" being notched 4" down on the lower course, thus giving a level 
floor for the masonry. The length of the piles, after being driven and cut 
off, was from 29 to 33 feet. The fall of the hammer at the last blow was 
from 35' 8" to 36'. The diameter of the piles was from 12 to 16 inches 
at the butt and 9 J to 14 inches at the smaller end. The last penetrations 
were from 2 J to 6 J inches. These facts apply to 39 piles given as examples 
and illustrations of the whole. The hammer weighed 1,630 lbs. The 
weight of the spruce piles was about 39J- lbs. to the cubic foot. The pile 
weighed was rather more dry than the average. At least 40 lbs. to the cubic 
foot would be a proper average. 

The compressibility of the soil into which these piles were driven was 
about one-ninth (J) of its entire bulk. 

COLONEL MASON'S FORMULA FOR BEARING WEIGHT OF PILES. 
Colonel Mason deduces the folloiving formula from an investigation of 
the value of this foundation, or the amount of weight with which each pile 
may be loaded : Let h be the height of the fall of the hammer at the last 
blow, 8 the distance to which the pile penetrates at the last blow, 1,630 lbs. 
the weight of the hammer, 960 lbs. the weight of a pile 24 cubic feet, and 
joint weight of pile and hammer 2,590 lbs. ; g the force of gravity (32^,) or 
the velocity that gravity will generate in a second of time, and V2^ = 

velocity of hammer as it strikes the pile, - is ^ n ^ = 115.2, and we have 

for the value of the retarding force 1,630 X J|f# x 115 - 2 = 118 > 175 %> 
or 52.75 tons. Each pile was actually loaded with and supported the 
average weight of 28,575 lbs., or 12.75 tons, besides its own weight (960 lbs.) 
and that of the grillage, or about \ of that which the calculated force of 
resistance is capable of holding in equilibrio. 



22 

In the above case the velocity of the hammer at the moment of impact 
will be V 2 x 36 X 32-J- = 48.125 feet per second, and the velocity of 

h g 

the joint mass of hammer and pile will be 48.125 X ^ffg- = 30.3 feet per 

second = V, and the retarding force ■— will be |£| = ?^ = 1,468, 

the velocity that the retarding force is capable of destroying in a second 
of time on the joint mass of the pile and hammer is then 1,468 feet. 
But gravity is capable of generating on that mass a velocity of 32 J feet ; 
dividing 1,468 by 32J we have 45.63 as the ratio between the retarding 
force and the force of gravity. That is, the retarding force is capable of 
holding in equilibrio 45.63 times the joint weight of the pile and hammer, 
or 2,590 pounds X 45.63 = 118,181 pounds. This is within six (6) 

pounds of the previous result. The time (t) in this case will be t = y> = 

7". 5 2 

30'~3 = 97 °f a second. 

The same result may be obtained by dividing the velocity destroyed, 
viz, 30 ' . 3, by the velocity the force is capable of destroying in a second 

of time, viz, 1,468 ; or j^ = ^ on the supposition of a constant force 
during the short period that it takes to destroy the motion of the pile, 
instead of a retarding force. Colonel Mason concludes his memoir with 
the deduction that Fort Montgomery experience is in favor of a coefficient 
of stability of &fo when applied to the calculation under the supposition 
of a constant force, although it in reality, as a general rule, decreases by 
very small decrements towards the terminal penetration ; and hence, taking 
this coefficient as a constant, is erring on the safe side. For a more minute 
detail of Colonel Mason's investigation of this subject see papers on Prac- 
tical Engineering No. 5, by Colonel J. L. Mason, Corps of Engineers, U. 
S. Army, 1850. 

Major Sanders' experiments at Fort Delaware were made with a view of 
deducing a rule for foundation on compressible soils, without any firm sub- 
stratum lying within reach of piles, for calculating what weight each pile 
would bear with safety, by comparing the distance it was sunk at the last 
blow with the force of the blow, it being understood that the pile has been 
driven to such an extent that for a number of blows the penetration has 
been uniform for equal blows. To ascertain such a rule two sets of piles 
of four each were driven, and a platform built on their heads ; they were 
then loaded with blocks of stone piled regularly on the platform ; and at 
regular intervals of time the amount of subsidence caused by the weight, 
which was periodically augmented, was noticed. These piles were not 
driven through the alluvial; their points were about 20 feet from the sandy 
subsoil, so that their stability was due to the accumulated and constantly 
increasing resistance of the same medium. 



23 

In one experiment the four piles were driven to a depth of about 24 
feet each, with a pile-driver that struck 34 blows in a minute, with a ram of 
2,000 pounds, and a uniform fall of 6 feet. An artesian well sunk on this 
island in 1834 found mud continuously to a depth of 46 feet below low- 
water mark, then 20 feet of sand, then 30 feet of coarse sand containing 
shells. It then entered and penetrated for 47 feet a bed of marl, which 
contained bowlders. At the penetration of 24 feet, each of the blows of 
the ram drove them about an inch, or exactly -^ of the fall of the ram. 
The weight placed on them at first was about 60,700 pounds, (or about -J- of 
the product of the friction and the weight of the ram.) This weight caused 
♦a subsidence in 6 months of -£%■ of an inch, when 15,000 pounds were added 
without increasing the subsidence. Upon again increasing the weight till 
it reached 94,000 ' pounds, (the ratio corresponding to which was J,) the 
subsidence began again, and in a month had attained -^ of an inch, when 
it ceased, or at least made no progress during the ensuing three months. 
The next addition to the weight brought it to 107,500 pounds, and the 
ratio to about ^, and in a month increased the subsidence to -fy of an inch. 
The next addition raised the weight to 121,800 pounds, and the ratio to 
1:4.6. This weight remained upon the piles without alteration until three 
years and five months had elapsed. In the first eight months it had caused 
the subsidence to increase from -£% to -J-| of an inch; and this subsidence 
did not increase during the remaining two years and nine months of the 
period. During the ensuing seven months the weight was successively 
increased to 134,000, 147,000, 160,000, 174,000, and finally to 189,500 
pounds, (or 84.59 tons;) the ratios corresponding to which were respectively 
1:4.19, 1:3.81, 1:3.52, 1:3.23, and 1:2.969. Until the last weight was put 
on no additional subsidence was caused by the increased pressure. It will 
be seen that the weight, answering to the ratio of 1:4.6 above mentioned, 
remained upheld 3 years and 4 months without the slightest variation in 
the subsidence of the piles, although it was repeatedly added to, and the 
whole system jarred in doing so during that period. But upon laying of 
the last load of stone the subsidence again began, and at the end of the 
ensuing period of 1 year and 5 months had arrived at ff of an inch.. This 
subsidence did not go on uniformly, but by steps at a time. It seemed 
to be ceasing at the end of the period, judging from the facts that the 
intervals of rest were longer and the successive subsidence less towards that 
date, viz : April 12, 1856. The next time that the observations were made 
on the levels of the pile heads was on the 24th of April, 1860. The sub- 
sidence had then arrived at an average of 1 inch within an appreciable 
fraction, showing an increase in 5 years and 5 months of ^ °^ an i ncn « 
It is probable that this subsidence took place within the 2 or 3 years that 
followed the date of April 12, 1856, and that the piles have remained im- 
movable for the last 2 years at least. 



24 

The whole period over which this experiment extended was (May, 1860) 
about 9 J years. The conclusions that may be derived from it are obvious ; 
that the subsidence had ceased may be safely assumed. It follows that a 
building on piles, driven in soils exactly of the nature of that in which 
these experimental piles were placed, will be safe if we do not load them 
with a greater weight than the third part of the quotient arising from dividing 
the product of the iveight of the ram and the distance it falls by the distance the 
pile is sunh by the last blow. The coefficient was, however, fixed by Major 
Sailders for safety at |. Conversely, having given the. weight of the 
superstructure, we can by the same rule ascertain the minimum number 
of piles that will sustain it if driven to a fixed depth, or the depth to which 
an approximately fixed number of piles must be driven to effect the same 
purpose. 

There were two experiments of the kind we have described made at 
Fort Delaware. The second one continued 3J- years, had similar results, 
and was equally regarded in the determination of the coefficient used in the 
rule. 

From other experiments made during the same period, Major Sanders 
ascertained the relation between the living force of the ram. and the dis- 
tance the pile is sunk for different falls by a series of experiments on 64 
piles, which received 1,900 blows from a ram of 800 pounds. It was 
found that when the fall was less than 3 feet, the useful effect was extremely 
small ; that it gained in a rapidly increasing ratio as the fall was augmented, 
a foot at the time, to 5 feet ; and at this point the ratio of useful effect to 
the force expended is at its maximum, and that the piles are driven to 
distances proportional to the blow ; or, in other words, that there is nothing 
gained by increasing the fall beyond 5 feet — for example, 2 blows of 5 feet 
will sink a pile as much as 1 blow of 10 feet; 3 blows as much as 1 of 15 
feet ; 4 blows of 5 feet as much as 1 of 20 feet. It was also found that if 
the 5-foot blows followed each other in rapid succession the useful effect 
was rather greater than if the interval employed in common hand-power 
machines for hoisting the ram was allowed to elapse. 

From 1833 to 1838 eleven thousand (11,000) piles, of 45 feet in length, 
12 inches square at the head and not less than 10 inches diameter at the 
small end, were driven for the foundations of Fort Delaware, under the 
superintendence of Captain Delafield, of the Corps of Engineers, with 
a hammer of 1,800 pounds, by blows in quick succession, with steam 
power — the maximum fall of the hammer being 45 feet. Since 1850, four 
thousand five hundred (4,500) additional piles were driven under Major 
Sanders' superintendence, from which experience he has drawn the pre- 
ceding deductions. Six thousand six hundred of these piles are under the 
scarps and casemates of the present work. (See Lieut. Morton's Life and 
Services of Major John Sanders, of the Corps of Engineers, 1861.) 



25 

In 1848 the excavations for the foundations of the work existing at this 
time (1868) were commenced and completed in 1849, and the piling by 
Major Sanders, heretofore referred to, was finished in 1851. By 1853 
two thousand tons of masonry had been laid on these piled foundations, 
and in 1859 the walls, arches, and other masonry were finished. 

Three bench marks were established in 1854, reference to which was 
made in 1859, when it was found the masonry had not settled in any part. 

From 1859 to October, 1866, the settlement on reference to the above 
bench marks was 4" at the maximum point, and 2 ".65 at the minimum, 
and a mean settlement for all the obseryed points of 3 // .19. No crack was 
perceptible in any part of the work in 1866 or in 1868. (See Reports of 
Superintendent at Fort Delaware.) 

RESISTANCE OF PILES DRIVEN AT THE S. W. PASS OF THE MISSISSIPPI 
RIVER, ON STAKE ISLAND. 

Stake Island consists of two mud lumps, forming its northwest and 
southeast extremities, about 500 yards apart. At both points the ground 
is high, of the character of other mud lumps. 

The space between the two mud lumps is much lower, presenting the 
same general features and vegetation as the land on either side of the 
river. The ground between these two lumps is about as solid as anywhere 
higher up on the river between the passes and the city. The experimental 
pile driving commenced on the 19th November, 1867. 

Pile No. 1 was 30 feet long. After 12 blows the head of the pile, 
within V 6 r/ of the ground, was rent to pieces. The head of the pile was 
square timber, 11 inches at the upper end and 10 inches diameter at the 
lower end, banded with J-inch iron 3J inches wide. Outside diameter 
9 J inches. The broken part of the pile was then cut off, and a piece 15 
feet long set on top of it. 17 more blows were then given, when the pile 
gave way, tearing the head completely off. The total depth obtained by 
these 29 blows was 41 ' 11", being driven to low- water mark, and level 
with the lowest soil. 

Pile No. 2, after 12 blows, was broken at the head, cut off, and a piece 
of 17 feet in length set upon it. 23 additional blows drove the pile down 
to 45' V below the surface of the ground. 

Pile No. 3, 30 feet long. After 11 blows the head of the pile was 
badly rent 4 r 6" above ground. 3' 9 r/ were cut off, and a piece of 18' 6^ 
set on, when with 9 blows the head gave* way. 5' V was then cut off, 
and with 7 more blows the pile was 35' 8" below the surface. 

Pile No. 4 was the same size as the previous piles. After 10 blows the 
head was V 8" above ground, and was then cut off and 16 feet set on; 
27 more blows were given, and V 9" cut off; when a piece of 16 feet 
was set on, and after 13 more blows 4 feet were cut off, leaving the pile 
54' 2" in the ground and 5 inches above. 



26 

The maximum fall of the hammer was 28 feet. The size of the ham- 
mer, of cast iron, was about 2' 5" high, V 8" wide, and V 1" thick. 
The penetration of these piles was as follows : 
No. 1, with the first blow falling 5' 9", was 6' 3". 
a 2 u " (i V ft /r u 7 ; & r/ 

" 3, " " " 4' 3", " 9' 1". 

" 4, « " " 3' 6", " 11' 4". 

]STo. 1, with the last blow falling 28 / 5 /r , was 10 inches. 
" 2, " " " 28' 7", " 11 inches. 

" 3, " " " 26' 6", " 9 inches. 

" 4, " « « 25 r 5 ;/ , " 14 inches. 

See Bonzano to Gen. McAlester, 9th January, 1868. 
In March, April, and May, 1868, 45 piles, of 50 to 60 feet in length, 
were driven under the direction of General McAlester, at St. Joseph's 
Island, in the same alluvial soil as deposited from the Mississippi river. 
The same remarkable uniformity of penetration, by the successive blows, 
was developed as at Stake Island. See McAlester's report of 5th May, 
1868. 

GRILLAGE FOUNDATIONS. 

A third system of foundations for compressible soils is that of the 
grillage, resting 'on the natural formation on the surface or at any selected 
depth. 

The following are examples of this character by engineers who have 
constructed many edifices on this principle in the United States : 

The earliest structure of this character, of which the writer has infor- 
mation, is a building at the Balize Bayou of the Mississippi river, near 
the site of the pilot houses. It is of brick masonry, constructed by the 
Spaniards or French during the early settlement of the country, and 
apparently for a magazine. It had settled so deep, up to the year 1829, 
as to make it impracticable, at that time, to ascertain the uses to which it 
may have been applied. From the practice of the inhabitants of the 
country it is inferred, in the absence of positive knowledge, that a grillage 
was used in this case. 

In 1807 a survey of the coast of the Mississippi had been made and the 
outlets of the Mississippi particularly examined to select the most eligible 
site, best material, and plan fo^ a light-house. A commission, appointed 
by the President of the United States, in 1816, again explored the various 
mouths of the river and the different islands situated there, and concluded 
that the most proper situation was at the mouth of the Northeast Pass of the 
Mississippi river, on Frank's Island. They say "this site appears to have 
undergone all the changes experienced by. the different islands here in the 
course of their formation and consolidation, being elevated about 3 feet 



27 

above the surface of the river , and the only island not covered with water 
during; the last hurricane." They bored the island and found the soil, for 
35 feet, a mixture of clay and fine sand, and to the depth of 50 feet, a 
dark-blue clay without any mixture of sand or vegetable matter. This clay 
grew harder as the borings descended. This commission designed a plan 
for this locality, the structure to be built of stone and brick, recommend- 
ing that for a foundation, the surface to be covered by a light-house, be 
dug down to the level of low water, and this space be filled with piles 25 
feet long, one foot diameter, driven as close as possible, and as long as they 
can be forced down with the " battering ram" then cut off at the surface 
of the water, laying upon their heads one foot square timber of the greatest 
length that could possibly be procured, and not more than V 6" apart, 
crossing these with another layer of the same dimensions, filling the inter- 
vals between the timbers with shells, or rubbish beaten down and united 
by pouring in grout; covering this with a close floor of 4-inch plank, 
spiked to the timbers. Upon the floor the foundations may be laid, taking 
the precaution to turn reversed arches under all the walls. The weight to 
be diminished comparatively by making it bear on the greatest surface pos- 
sible. (See State Papers on Commerce and Agriculture.) 

A light-house of stone and brick masonry was afterwards built at this 
locality. After being finished it soon settled irregularly, and finally 
inclined to one side so much as to make it necessary to 1 take down the 
whole structure before the year 1824. Soon after which period the 
material was in part transported to and used in the construction of Fort 
Jackson, about thirty miles up the river. By reference to the original 
drawings of Mr. Latrobe, (who constructed the building,) and loaned me 
.by his brother, Benj. H. Latrobe, of Baltimore, it appears that the masonry 
of this tower was 81 J- feet high, and 19 feet diameter at the base, resting 
on 53 piles of ten feet in length. 

The foundations of Fort Pike, on the Rigolets, were commenced about 
the year 1820. The soil is very similar to that at the mouths of the 
Mississippi, the surface being mostly vegetable matter underlaid by a com- 
bination of vegetable earths and dark clay. The foundations of the scarps 
and piers of the casemates were all laid on a grillage of round pine logs, 
side by side, resting on the excavated soil, and crossed on top, at right 
angles, by similar logs of from 10 to 12 inches diameter, and about two 
feet apart in the clear. The masonry of the piers was built in and thus 
united to the masonry of the scarps. The work was finished about the 
year 1828. The foundations are about six feet below the level of the 
waters of Lake Pontchartrain, and the ground below that level is saturated 
with water. 

The work settled irregularly* The masonry of the casemate piers broke 
from the scarps, making cracks about 4 inches Avide. The timber grillage 



28 

in this case failed to overcome the compressibility of the subsoil or to 
preserve uniformity of settlement. (Personal recollection.) 

Fort Wood, on the Chef Menteur Pass, (La.,) (now, 1868,'Fort Macomb,) 
was commenced about the year 1825 and finished in 1832. It is situated 
at the end of a dry clay ridge following the bank of the Metairie Bayou, 
from near New Orleans, to the entrance of this bayou into Pass Chef Men- 
teur, and is the firmest soil on which any of the forts in Louisiana are con- 
structed, the natural surface being 3 feet above the waters of the Pass and 
Lakes Pontchartrain and Borgne. This dry ridge is wooded with heavy 
live-oak timber. The foundations of the scarps and casemates are similar 
to those of the fort on the Rigolets, and the general plan of the work similar. 
It was finished about the year 1832. The foundations were about six feet 
below water, and the ground saturated from the lake' level to the depth of 
the excavations. The excavations were in a firm adhesive clay soil; hand 
pumps and buckets sufficed to keep down the water during the excavations. 

In this case there was no such irregularity of subsidence as to injure the 
work, although extensive repairs were necessary in consequence of this 
irregularity. The grillage did not suffice to overcome the compressibility 
of the subsoil or preserve uniformity in the levels of the masonry. (Per- 
sonal recollection.) 

The foundations of Fort Jackson, Placquemine bend of the Mississippi 
river, were commenced in 1825; the masonry was finished and ramparts 
formed, ready to receive the parapets, in 1832, at which time the work 
was suspended to give time for settlement. The subsoil in this case is very 
compressible, and saturated with water at all times from near the surface to 
and below the bottom of the foundations, about 11 feet below the natural 
level of the country. Vegetable matter composed the upper layers, under 
which it is combined with dark clay. The problem in this case was to 
create uniformity of pressure and settlement by underlaying the masonry 
with a strong grillage of timber laid on a plank floor. The plank was laid 
on the excavated earth, and large cypress timber, 12 inches thick, 15 to 24 
inches wide, laid longitudinally upon it, edge and edge, formed a solid con- 
tinuous floor. On the top of this solid flooring other timbers, 1 2 inches thick, 
and from 15 to 18 inches wide, were^laid 3 feet from centres, perpendicu- 
lar to the lower courses. The spaces between these last timbers were filled, 
solid, with brick masonry laid in cement mortar. This grillage projected 
three feet in front and rear of the fair masonry of the scarps, which were 
from 8 to 10 feet thick. The grillage and foundations of the casemates 
were constructed in like manner. The result, seven years after the com- 
mencement of the foundations, was unequal settlement of various parts of 
the work, and cracks in the masonry of the scarps on the faces and flanks 
of the bastions. It became necessary to lighten the load of embankment 
pressing on the foundations. The earth pressing against the centre of the 



29 

scarps of the bastion faces and of the solid curtains was removed to 'the 
depth of the grillage of the casemates, and hollow vertical brick cylinders, 
of 18 feet diameter, covered with hemispheres of brick masonry, were con- 
structed behind the faces of the bastions, and three horizontal bomb-proof 
storerooms were built on the centres of the solid curtains. 

No stronger or more substantial grillage is known to have been constructed 
in Louisiana. In 1842 the casemates of the two water fronts and gate- way 
fronts were a second time loaded with an excess of weight to restore the 
levels and guard against future inequality of settlement. In 1851 the 
floors of the casemates of the flanks had to be raised and other repairs 
made, in consequence of unequal settlement. 

The grillage failed to preserve uniformity of settlement, and the com- 
pression of the subsoil was not overcome by this application of a timber 
platform distributing the weight over a great surface. (Personal knowledge.) 

Battery Bienvenue, on the bayou of this name, emptying into Lake 
Borgne, was commenced about the year 1828. It is founded upon a grillage 
of round pine logs, averaging 12 inches diameter, laid on a plank floor, and 
overlaid by 12-inch pine logs at right angles to the lower layer, and distant 
about 3 feet from centres. This grillage is founded four feet below the 
surface of the water of the bayou. The soil is but little better than a 
prairie tremblante. Borings were made 20 feet deep, indicating vegetable 
soil only, combined with a large percentage of water. The grillage is ar- 
ranged precisely similar to those of Chef Menteur and the Bigolets. The 
masonry consists of a low scarp, backed by an earthen rampart. The 
masonry settled several feet before the scarp was finished, with great irregu- 
larities ; the centre of each line of the trace of the work settling some feet 
below the ends. A square magazine, built on an independent grillage, 
similar to that under the scarps, settled, soon after the bomb-proof arch 
was turned, several feet, bringing the lintel of the door- way down to the 
surface of the ground. In this case the grillage failed to either secure a 
uniformity of settlement or overcome the compressibility even to such an 
extent as to fulfill the desired useful purpose. Great and extensive repairs 
and additions have been since made to this work. (Personal recollection.) 

■Southwest Pass Light-lwuse was built in 1831. It is about 65 feet high, 
and built of wood. It rests on a timber grillage of unknown dimensions. 
It has failed to secure the conditions necessary for a foundation and has 
now to be rebuilt, having inclined so far from the vertical as to render a 
hastened reconstruction desirable. The site of this light-house is on one of 
the upheaved islands common to the mouth of this river. (Records of the 
Light-house Board.) 

The St. Charles Hotel, in the city of New Orleans, was commenced in 
1836 and finished in 1837. It was destroyed by fire in 1851. The 
foundations were of brick masonry, on a grillage of heavy flat-boat gun- 



30 

waifs of 60 to 80 feet in length, 20 to 30 inches wide, and 6 to 12 inches 
thick, and laid about 6 feet below the sidewalk. This building settled 2 
feet in 12 or 14 years. The present hotel (1868) was commenced in 1851, 
on top of the old foundations, and finished in 1853. It has settled fully 
12 inches more (in addition to the settlement of the former building) in the 
last 15 years, making a total compressibility of the subsoil of 3 feet since 
1837, or in 31 years. In this case a grillage has failed to secure the desired 
object. (Henry Howard to General Delafield, June, 1868.) 

The Light-house at Pass a V Outre was built in 1855* It is a cast-iron 
shell, about 65 feet high, resting upon a masonry base 4' 6" thick, ex- 
tending a like distance (4' 6 r/ ) beyond the base of the tower and under the 
whole structure. In 1864 an interior brick lining was added. It is not 
known that any timber underlays the masonry. This masonry, however, 
covering the entire surface occupied by the building, with 4' 6 /r offsets 
beyond it, fulfills all the conditions of underlaying timbers. The site on 
which it is built is firm on the surface and is about 3 feet above the level 
of the Gulf of Mexico. It must, therefore, be upon one of the upheaved 
islands common at the outlets of the Mississippi. It has settled unequally, 
one side leaning from 9 to 12 inches in its height. 

In this case the grillage or masonry base has failed to secure either 
uniformity of settlement or to overcome the compressibility. The keeper's 
house at this locality is a lj-story wooden structure, resting on 9 brick 
piers of 18 inches square each, under which is a grillage 6 feet square, of 
two thicknesses of round logs. It has settled 2J feet and now requires 
repairs (1868) to correct the consequent defects. The grillage has in this 
case failed to secure the desired stability. (Bonzano's report to the Light- 
house Board, Washington.) 

The First Presbyterian Church, in New Orleans, was commenced in 
1846 and finished in 1857. The main tower is 20 feet square and 115 
feet high, surmounted with a wooden spire. The foundations were built 
of brick masonry, laid in cement mortar, on a grillage of two thicknesses 
of flat-boat gunwales of forty-five feet in length, crossing one another. 
The excavation was 12 feet below the surface of the street. The bottom 
was a hard, stiff, blue clay, the best my informant has ever seen, after 
thirty years' practice as an architect in New Orleans. It has settled 5 J 
inches in 11 years. (Henry Howard to Gen. Delafield, June 1868.) 

Fort Calhoun, now Fort Wool, Hampton Roads, Va., was commenced in 
April, 1819, when the first stone was deposited on the Rip-rap shoal for 
its foundation, in 21 feet water. The shoal and adjacent shores of the 
Chesapeake Bay and Hampton Roads are hard sand. It was determined to 
construct the superstructure of a four-tier casemated masonry battery at 
this locality, on an enrockment of quarry stone, thus forming an island 
similar to the Plymouth and Cherbourg breakwaters. During the first 
year's labor the enrockment was brought to the surface of the water on the 



31 

line of the southern face of the work, and in 1824 the surface had been 
enlarged to receive the entire foundations of the superstructure, for which 
preparations were made and commenced in 1826. The enrockment was 
added to, and an area of several acres was formed, terminating with a long 
slope, to intersect the shoal; equivalent to a grillage for the proposed 
superstructure, spreading the pressure of the walls at least 25 feet beyond 
their exterior lines. The foundations of the casemates on the water fronts 
were all laid, and the scarps and piers of the casemates raised to the spring- 
ing lines of the arches of the embrasures, when numerous cracks in the 
masonry and irregular settlement of the work throughout its whole extent 
indicated that the foundations could not be relied upon. It was determined 
to suspend the construction of the work in 1829 or 1830, and load the 
foundations of the scarps and casemates with a weight greater than that of 
the castle in its finished state, with its armament, stores, and garrison. 

In 1833, eleven thousand (11,000) tons of building stone were piled 
over and near the walls, bearing on their foundations. 

In 1834, sixty-one thousand eight hundred and sixty-six tons (61,866) 
were added. The annual subsidence with this increased weight at the 
centre of the work was J less than it was in 1833, and those parts that 
formerly settled most now settled least. 

In 1835, twenty thousand tons more than the estimated required quantity 
was resting upon and along the whole extent of the foundations. This acces- 
sion of weight continued to cause subsidence, though in a decreasing ratio. 

In July, 1836, the stone for the superstructure and materials accumulated 
for compressing the foundations were being removed, upon the supposition 
that the base on which the castle was to rest had been satisfactorily com- 
pressed. In 1837 the load of stone was entirely removed from the founda- 
tions; continued subsidence was, however, observed, and the foundations 
were immediately reloaded. 

In 1840, a total weight of 55,716 tons had been reloaded on the founda- 
tions, increased subsidence was still observed. In November, 1842, there 
was an excess of 13,627 tons on the foundations, beyond the ultimate 
weight to be supported. The average subsidence in 1841 was f of an 
inch; compared with former years it was in a decreasing ratio. In 1843 
it was found that the mass was still settling, when an additional load was 
recommended. In 1846 the subsidence was f of an inch, and up to 1850 
the diminution of settlement was progressive. 

The total average subsidence of the foundations from 1830 to 1856, 
accurately noted from year to year, was at the greatest point 5.28 feet, and 
at the least 4.35 feet. It was immovable from 1850 to 1856. From 1841 
to 1847 the maximum average settlement was -j-J-^- of a foot. The total 
subsidence of a tide pier from 1824 to 1851 was 6.63 feet. (See Annual 
Reports of Chief Engineers, accompanying President's Message.) 



32 

Custom-house, New Orleans, (La.) This building was conimenced in 
1848, and progressed from time to time until 1860. It is founded upon a 
flooring of plank laid on the excavation seven feet below the street pave- 
ment. On this floor a timber grillage is lai4 of 12-inch logs, "side and 
side," over which similar logs are placed transversely, distant from each 
other 2 to 3 feet in the clear. 

The space between the timbers is filled with concrete, which is continued 
over the whole grillage for a depth of one foot. Counter arches of 1J 
bricks thick support the walls of the interior subdivisions of the building, 
thus throwing the weight of the building upon the entire surface included 
within the outline of the building. 

As a concrete and grillage foundation to support this heavy building, no 
greater surface, to resist the weight and pressure of the walls, could well 
be attained. 

The walls of 2' 6" thick rest on grillage timbers 10 ft. wide. 

Those of 4' " " "15 ft. " 

And those of 9' " " " 20 ft. "(abutments.) 

In 1860 the granite walls of this building had been carried up 75 feet 
above the concrete base to the architrave line of the entablature, and all 
the iron floor beams of the fourth story finished. 

The exterior walls are four feet thick, exclusive of projections; 2 J feet 
of which is brick masonry, and 1 J feet of stone masonry. 

In 1851 a commission reported that borings at the custom-house, and at 
a point not far removed from it, indicated different degrees of compressi- 
bility. It is situated upon the firmest, dryest, and most reliable ground 
in and about the city of New Orleans. 

The maximum settlement of the building in any one point, up to 1860, 
was 2' 6". This compressibility of the soil beneath the grillage was very 
variable. 

From 1848 to 1851 the maximum settlement was 22.57 inches, and the 
minimum in the same time was 15.63, making a difference of level in 
various parts of the building of 6.94 inches. 

In the year 1857-58, the maximum settlement was 3.50 inches, and the 
minimum 0.66, making a difference of settlement this year of 2.84 inches; 
and in 1858-59, the maximum was 2.63 inches, and in many places 
nothing, making a difference of settlement, level and compressibility, this 
year of 2.63 inches. 

The line of the exterior walls in 1864, on which the temporary roof 
rests, varies in the level 3 inches. 

This grillage covers a surface of about 300 feet square, and although 
well constructed, and with great care, it has failed in its objects. (See 
Records of the Treasury Department, Bureau of the Architect.) 



33 

Foi f t Sumter, Harbor of Charleston, was constructed upon an enrock- 
ment similar to Fort Calhoun, now Fort Wool. In 1840 the settlement 
was such as to induce the superintending engineer to recommend that it be 
loaded with a weight equal to the maximum, with its armament and mu- 
nitions, that could rest upon its foundations. In 1850, the engineers 
reported the subsidence of this work to be continuous, though in a decreas- 
ing ratio annually. At this time the scarps and two tiers of casemate 
arches were completed. 

CONCLUSION. 

The plan proposed by a committee of the Light-house Board, in 1868, 
is again referred to the same committee, increased by two other members 
of the board to consider the whole subject anew. The plan then approved 
by the board is appended hereto ; which, with the practice and views of 
many experienced engineers in compressible soils, is presented, with the 
belief that the best plan suited to this most difficult locality may be more 
satisfactorily devised with the information now embodied in this memoir 
for the consideration of the committee. 

Extracts: "Considering the impracticability of finding any solid natural 
base at the outlets of the Mississippi, or any locality calculated to sustain 
the weight of an iron light-house, without extraordinary aids from art; 
and the extraordinary geological formation of the country about the Passes 
of the Mississippi, all going to show that great and unusual precautions are 
necessary to secure a foundation for any weighty structure at or about the 
outlets of the Mississippi, the committee proposes some modifications of the 
plans submitted to it, with the hope of securing greater solidity, and to a 
greater depth of the natural soil to resist the settling of an iron light-house 
for the proposed locality at the Southwest Pass." 

" The first precaution is that the superstructure to rest on this founda- 
tion shall be of the least practicable weight to fulfill all the conditions for a 
permanent light-house, and then that the soil of the selected site be solidi- 
fied to the greatest practicable depth by wedging it with wooden (pine) 
piles of about 50 feet in length, not less than 12 inches square at the head 
and not less than 10 inches diameter at the lower end, driven into the soil 
with a hammer of not less than 1,800 lbs. weight, with a final fall of 45 
feet, continuing the operation of driving until the head of the pile may 
pass below the ways of the pile engine, and thence by a punch to the sur- 
face of the soil, or until the head of the pile, battered into fibres, no 
longer transmits the percussive action of the ram to the solid wood of the 
pile. These piles should be driven in rows, 3 r 6 /r from centres, through- 
out the entire surface of the site to be occupied. After driving this series 
of piles a judgment can be formed of the practicability of giving additional 
solidity to the natural soil by driving another series of piles of the same 



34 

dimensions (or somewhat smaller diameter) at the intersection of the 
diagonal lines drawn from the heads of four consecutive piles of the first 
series, and 3' 6 r/ from their own centres in their own parallel lines or 
roads/' 

"No more timber than of these two series can probably be driven into 
the soil. Should the contrary be the case, the site should be abandoned as 
approaching too near a semi-fluid to justify the construction of any per- 
manent structure thereon." 

"Having thus solidified the soil by wedging with timber, the heads of 
all the piles of the first series are to be cut off level, to a uniform depth of 
2' 6" below the lowest low water, and the heads of the second series to a 
uniform level of V 6" below the lowest low water." 

"The next operation will be to secure the heads of all those piles in a 
fixed position in relation to each other, and from being inclined by the 
superincumbent weight of the light-house. This will be effected by exca- 
vating the soil to a depth of V 6" below the heads of the first series of 
piles cut to a uniform level as above required; (it may be found more 
advantageous to make this excavation before driving any piles, to admit of 
floating the pile engine on a scow, a great economy where practicable;) or, 
to a depth of 4 feet below the lowest low water." 

" The space below and between the heads of the first series of piles to 
the depth of V 6 r/ will then be filled with concrete to the heads, care being 
taken to pump out all the water, that the concrete can be rammed thor- 
oughly between the piles and into the soil on which it is first deposited. 
This concrete will be brought to the level of the heads of this series of 
piles, thus bracing them from each other by a hard, durable, and continuous 
mass of concrete of V 6 /r thick over the whole surface of the foundation." 

"Over the heads of this first series of piles, and resting also upon the 
concrete surface between them, horizontal timbers (cypress or pine) will be 
laid, 12 inches thick by 15 to 18 inches wide, when another layer of con- 
crete will be rammed about these string pieces and the heads of the second 
series of piles; then a row of horizontal 12-inch timbers at right angles 
with the first, of 15 to 18 inches wide, will be laid over the heads of the 
second series of piles, and concrete filled in solid to the surface of the 
second layer of horizontal bearing pieces. The string pieces resting on the 
heads of the piles may be treenailed thereto to keep them in place while the 
work is being constructed." 

"We have now solidified the soil to a depth of 50 feet, and above it 
formed a solid floor of timber and concrete, resting upon and covering the 
entire base thus solidified by wedging." 

"Upon this last surface, which is 6 inches below the lowest low water, 
completely excluded from the air, the foundation of the masonry for the 
support of the iron of the superstructure will be commenced." 



35 

The foundation of the base of the iron work should be four feet above 
ordinary high water. "This foundation, down to the level of the timber 
grillage, should be formed of solid brick or stone masonry, spreading out 
to cover the greatest possible surface, by offsets in every course of brick or 
stone of which this part may be constructed. Between this exterior base 
and the centre, the entire foundation will be raised with concrete to the 
natural level of the shoal. As these parts cannot have any weight of the 
superstructure (of the proposed design) upon them, any superfluous mass of 
material but adds to the risk of settling. " 

"The superstructure should be designed to throw the weight not only on 
the corner posts, but upon the spaces from one of these corners to the other, 
and also upon the radii connecting these corners with the centre column. 
With this in view the masonry on these lines, from the timber platform, 
should be built with offsets to cover as much surface as practicable. The 
bed-plate of the superstructure resting on the masonry should be bolted 
with composition bolts, securing them to the under part of the concrete and 
timber platform, to give some additional stability to the base against the 
action of the wind.' 7 

"Notwithstanding all these precautions, it is considered advisable, pre- 
viously to raising the superstructure, to load the entire surface of this 
artificial foundation with a weight of matter greater than the entire load it 
can ever be required to sustain. This load should remain at least one 
year, when an examination should be made as to the propriety of commenc- 
ing the superstructure, suspending the work, adding to the load and await 
another year, or abandon the site altogether." 

The weight of cast and wrought-iron of the superstructure of the plan 
submitted to the committee is 400,000 lbs. This may be greatly reduced 
by the adoption of modification of the design of the framing of the wrought- 
iron work. Reference to the Practice of European Engineers for such 
structures may be found in Proceedings of the Institution of Mechanical 
Engineers for 1861, giving a detailed description of the light-house at 
Buda, Spain. Minutes of Proceedings of the Institution of Civil Engi- 
neers, vol. 23, for a description of the Ushruffee light-house in the Red 
Sea, and the Engineers' and Architects' Journal for Jan. 7, 1868, for 
description of the light-house for the Douvres. 

RICH'D DELAFIELD, 

Brevet Major General, 
Corps of Engineers, U. 8. Army. 



LIBRARY OF CONGRESS 



020 578 733 1 



LIBRARY OF CONGRESS 



7" 020 578 733 1 * 



